1. Field of the Invention
The present invention is related generally to heat exchangers and, more particularly, to heat exchangers which incorporate fin and tube or plate and tube arrangements. Even more specifically, the present invention is related to the use of jet impingement holes through the fins or plates of the heat exchanger and, most particularly, to the use of these jet impingement holes which are shaped in the form of an oblong, or oval, with a cusp surface which creates a vortex-type flow of fluid as the fluid passes through the holes of the fins.
2. Description of the Prior Art
Those skilled in the art have been aware of tube and fin heat exchangers for many years. In addition, those skilled artisans are also generally familiar with the concept of impingement cooling devices. Furthermore, certain cooling applications have utilized vortex generating flow passages for the purposes of increasing film-cooling effectiveness and surface coverage.
U.S. Pat. No. 3,844,343, which issued to Burggraf on Oct. 29, 1974, discloses an impingement cooling system that incorporates a heated plate which is cooled by a cooling fluid impinging thereon. The cooling fluid flows from a plenum that is partially defined by a second plate spaced away from the first plate. Apertures in the latter plate provide communication between the plenum and the cooled plates. For the purpose of increasing cool fluid heat transfer of the impinging jets, each of the apertures is provided with a varied diameter along its length, the smallest diameter extending over a given portion of the aperture length to form a throat portion. The aperture cross section between the throat and the maximum diameter may be of any convenient configuration, such as conical or counterbored.
U.S. Pat. No. 2,474,467, which issued to Conley on June 28, 1949, describes a heating apparatus wherein a source of heat is placed at the bottom of the unit and the air immediately above the unit of heat is heated within an enlarged heat transfer chamber. Transverse passageways of the chamber are provided whereby heat is transferred to air current circulating throughout the room or other area which the apparatus is intended to heat. Such passageways are provided in the form of Venturi ducts with lateral wing areas which not only cause the heated gasses from the source of heat to follow a tortuous passageway to the flue or chimney into which such gasses are discharged, but also causes a spiral jet action on the air within the chamber.
U.S. Pat. No. 3,741,285, which issued to Kuethe on June 26, 1973, describes a boundary layer control of flow separation and heat exchange. The purpose of this invention is to provide boundary layer control for the delay or prevention of flow separation and to increase the rate of heat exchange between the surface and fluid by an arrangement of surface elements which may take the form of either crests or discrete concave depressions in the surface. These depressions have effective depth or dimensions of less than that of the adjacent boundary layer thickness for the purpose of causing the formation of vortices with succeeded surface elements being positioned to cause vortex amplification. This creates effective boundary layer mixing with less drag, weight penalty, noise and energy loss than conventional vane type generators.
U.S. Pat. No. 4,494,171, which issued to Bland et al on Jan. 15, 1985, describes an impingement cooling apparatus for a heat liberating device or cold plate. It relates to an impingement cooling apparatus for use in the removal of heat from a heat liberating device, such as an electronic component. The apparatus includes a housing on which the device is secured and a stack of plates fitted within the housing. One of the plates is an impingement orifice plate adjacent the housing where the device is located. The orifice plate has a region that is characterized by coolant flow impingement orifices passing therethrough. The orifice plate also has a coolant drainage return adjacent the impingement orifice region.
U.S. Pat. No. 4,573,865, which issued to Hsia et al on Mar. 4, 1986, discloses a multiple impingement cooled structure. This patent describes a structure, such as for use as a turbine shroud assembly. It includes a plurality of baffles which define with an element to be cooled, such as a shroud, a plurality of cavities. Impingement cooling air is directed through holes in one of the baffles to impinge upon only the portion of the shroud in the first cavity. That cooling air is directed to impinge again upon the portion of the shroud in a second cavity.
U.S. Pat. No. 3,804,159, which issued to Searight et al on Apr. 16, 1974, describes a jet impingement fin coil. It discusses and illustrates a heat exchanger in the form of a finned tube configuration for transferring heat between the contents of the tube and the atmosphere surrounding the finned tube. The fins extend outwardly from the tube and are attached to the tube in heat conducting relationship. The fins are perforated in a predetermined pattern to provide openings through which the outside atmosphere is directed as jets upon portions of the fins in such a fashion as to disrupt boundary layers normally existing adjacent the surfaces upon which the jets impinge.
An article, titled "Vortex Generating Flow Passage Design For Increased Film-Cooling Effectiveness and Surface Coverage", by S. Stephen Papell of the National Aeronautics and Space Administration, Louis Research Center, was written for the ASME Journal. It describes the use of flow passages which have a cross section shaped in the form of an oval with two long sides in which one of the long sides is generally flat and the other long side is provided with a cusp surface. This shape induces counter rotating vortex pairs in the flow passing through the passage. This particular paper was written in relation to experiments conducted to examine the fluid mechanics of the basic discreet whole film cooling process described in the paper as an inclined jet in crossflow. The paper hypothesizes a cusp-shaped coolant flow channel contour that increases the efficiency of the film cooling process. The paper examines the interaction of the vortex structures generated by both geometry and crossflow in terms of film cooling effectiveness and surface coverage. Film cooling is a method for protecting turbine blades and vanes in high performance engines for advanced aircraft. The coolant itself is drawn from a compressor that is part of the aerodynamic cycle of the engine. The coolant enters the blade base to access the internal passages in the blade and is ejected through holes drilled at some angle through the blade walls into a flowing hot gas boundary layer along the outside surface of the blade. The injected coolant is trapped in the boundary layer and insulates the blade from the hot gases.
While those skilled in the art of heat exchange devices have utilized tube and fin heat exchangers to conduct heat from one fluid to another and, in addition, have utilized jet impingement techniques to transmit heat from a surface to a fluid, none of the prior art shows the combination of jet impingement techniques with plate and tube or fin and tube heat exchangers wherein the passages through the plates or fins of the heat exchanger are shaped to provide a cusp surface for the purpose of inducing counter rotating vortices in the fluid passing through the openings.